U.S. patent number 10,976,415 [Application Number 17/093,599] was granted by the patent office on 2021-04-13 for techniques for image conjugate pitch reduction.
This patent grant is currently assigned to AEVA, INC.. The grantee listed for this patent is AEVA, INC.. Invention is credited to Keith Gagne, Mina Rezk.
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United States Patent |
10,976,415 |
Gagne , et al. |
April 13, 2021 |
Techniques for image conjugate pitch reduction
Abstract
A light detection and ranging (LIDAR) system includes a first
optical source to generate a first optical beam and a second
optical source to generate a second optical beam. The first optical
beam and the second optical beam are separated by a first spacing.
The system further includes an optical system to receive the first
optical beam and the second optical beam and reduce the first
spacing between the first optical beam and the second optical beam
to a second spacing and an output lens to transmit the first and
second optical beams to scanner optics.
Inventors: |
Gagne; Keith (Santa Clara,
CA), Rezk; Mina (Haymarket, VA) |
Applicant: |
Name |
City |
State |
Country |
Type |
AEVA, INC. |
Mountain View |
CA |
US |
|
|
Assignee: |
AEVA, INC. (Mountain View,
CA)
|
Family
ID: |
1000005261620 |
Appl.
No.: |
17/093,599 |
Filed: |
November 9, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S
7/4817 (20130101); G01S 17/89 (20130101); G02B
26/108 (20130101); G01S 7/4815 (20130101); G02B
5/045 (20130101); G02B 27/30 (20130101) |
Current International
Class: |
G01S
7/481 (20060101); G01S 17/89 (20200101); G02B
26/10 (20060101); G02B 5/04 (20060101); G02B
27/30 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Xiao; Yuqing
Assistant Examiner: Askarian; Amir J
Attorney, Agent or Firm: Womble Bond Dickinson (US) LLP
Claims
What is claimed is:
1. A light detection and ranging (LIDAR) system comprising: a first
optical source to generate a first optical beam; a first
collimating lens to collimate the first optical beam; a first prism
wedge of the first prism wedge pair to redirect the first optical
beam; a first focusing lens to focus the first optical beam on a
front surface of a second prism wedge of the first prism wedge
pair, the second prism wedge to direct the first optical beam
toward the output lens; a second optical source to generate a
second optical beam, wherein the first optical beam and the second
optical beam are separated by a first spacing; an optical system to
receive the first optical beam and the second optical beam and
reduce the first spacing between the first optical beam and the
second optical beam to a second spacing, wherein the optical system
comprises a first prism wedge pair to modify a first decenter of
the first optical beam with respect to the output lens and a second
prism wedge pair to modify a second decenter of the second optical
beam with respect to the output lens; and an output lens to
transmit the first and second optical beams to scanner optics.
2. The LIDAR system of claim 1, wherein the optical system further
comprises: a second collimating lens to collimate the second
optical beam; a third prism wedge of the second prism wedge pair to
redirect the second optical beam; and a second focusing lens to
focus the second optical beam on a front surface of a fourth prism
wedge of the second prism wedge pair, the fourth prism wedge to
direct the second optical beam toward the output lens.
3. The LIDAR system of claim 2, wherein the second spacing of the
first and second optical beams is determined by an angle of the
first prism wedge pair and the second prism wedge pair and a first
focal length of the first focusing lens and a second focal length
of the second focusing lens.
4. The LIDAR system of claim 1, wherein the first collimating lens
is spaced a first distance from the first optical source, the first
distance corresponding to a focal length of the first collimating
lens.
5. The LIDAR system of claim 4, wherein the second prism wedge is
spaced a second distance from the first focusing lens, the second
distance corresponding to a focal length of the first focusing
lens.
6. The LIDAR system of claim 1, wherein the output lens creates an
angular separation between the first optical beam and the second
optical beam.
7. The LIDAR system of claim 6, wherein the angular separation
between the first optical beam and the second optical beam is less
than two degrees.
8. The LIDAR system of claim 6, wherein the angular separation
between the first and second optical beams is determined by the
second spacing of the first and second optical beams and a focal
length of the output lens.
9. A method, comprising: generating a first optical beam at a first
optical source and a second optical beam at a second optical
source, the first optical beam and the second optical beam being
separated by a first spacing; reducing, by an optical system, the
first spacing between the first optical beam and the second optical
beam to a second spacing, wherein the optical system comprises a
first prism wedge pair to modify a first decenter of the first
optical beam with respect to the output lens and a second prism
wedge pair to modify a second decenter of the second optical beam
with respect to the output lens; and transmitting the first optical
beam and the second optical beam to an output lens at the second
spacing, wherein reducing the first spacing between the first
optical beam and the second optical beam comprises: collimating the
first optical beam using a first collimating lens; redirecting the
first optical beam using a first prism wedge; focusing the first
optical beam on a second prism wedge using a first focusing lens;
and redirecting the first optical beam toward the output lens using
the second prism wedge.
10. The method of claim 9, wherein reducing the first spacing
between the first and second optical beams further comprises:
collimating the second optical beam using a second collimating
lens; redirecting the second optical beam using a third prism
wedge; focusing the second optical beam on a fourth prism wedge
using a second focusing lens; and redirecting the second optical
beam toward the output lens using the fourth prism wedge.
11. The method of claim 10, wherein the second spacing of the first
and second optical beams is determined by an angle of the first
prism wedge pair and the second prism wedge pair and a first focal
length of the first focusing lens and second focal length of the
second focusing lens.
12. The method of claim 9, wherein the first collimating lens is
spaced a first distance from the first optical source, the first
distance corresponding to a focal length of the first collimating
lens.
13. The method of claim 12, wherein the second prism wedge is
spaced a second distance from the first focusing lens, the second
distance corresponding to a focal length of the first focusing
lens.
14. The method of claim 9, further comprising: creating an angular
separation of the first optical beam and second optical beam using
the output lens.
15. The method of claim 14, wherein the angular separation is based
on the second spacing of the first optical beam and the second
optical beam.
16. The method of claim 14, wherein the angular separation between
the first optical beam and the second optical beam is less than two
degrees.
Description
FIELD OF INVENTION
The present disclosure is related to light detection and ranging
(LIDAR) systems in general, and more particularly to image
conjugate pitch reduction of a LIDAR system.
BACKGROUND
Frequency-Modulated Continuous-Wave (FMCW) LIDAR systems use
tunable lasers for frequency-chirped illumination of targets, and
coherent receivers for detection of backscattered or reflected
light from the targets that are combined with a local copy of the
transmitted signal (LO signal). Conventional LIDAR systems require
high frame rates and an increased number of scanning points
typically achieved by using multiple numbers of optical sources to
emit optical beams. The optical sources may be placed in a
one-dimensional or two-dimensional array separated by some
distance, referred to as pitch. The array of optical sources may
share a single output lens. The single output lens provides angular
separation between collimated optical beams to create discrete
lines after reaching the scanner of the LIDAR system. Using the
single output lens for multiple optical beams may reduce the cost
form factor of the system in comparison to adding additional output
lenses. However, as more optical beams are added to the system
using a single output lens, the decenter of the beams on the output
lens is increased, resulting in changes in numerical aperture (NA)
of the system as well as an increase in aberration content of the
output beams.
SUMMARY
The present disclosure describes various examples of LIDAR systems
and methods for image conjugate pitch reduction.
In some embodiments, a light detection and ranging (LIDAR) system
includes a first optical source to generate a first optical beam
and a second optical source to generate a second optical beam,
wherein the first optical beam and the second optical beam are
separated by a first spacing. The LIDAR system further includes an
optical system to receive the first optical beam and the second
optical beam and reduce the first spacing between the first optical
beam and the second optical beam to a second spacing and an output
lens to transmit the first and second optical beams to scanner
optics.
In some embodiments, the optical system includes a first prism
wedge pair to modify a first decenter of the first optical beam
with respect to the output lens and a second prism wedge pair to
modify a second decenter of the second optical beam with respect to
the output lens. In some embodiment, the optical system further
includes a first collimating lens to collimate the first optical
beam, a first prism wedge of the first prism wedge pair to redirect
the first optical beam, and a first focusing lens to focus the
first optical beam on a front surface of a second prism wedge of
the first prism wedge pair, the second prism wedge to direct the
first optical beam toward the output lens.
In some embodiments, the optical system includes a second
collimating lens to collimate the second optical beam, a third
prism wedge of the second prism wedge pair to redirect the second
optical beam, and a second focusing lens to focus the second
optical beam on a front surface of a fourth prism wedge of the
second prism wedge pair, the fourth prism wedge to direct the
second optical beam toward the output lens. In some embodiments,
the second spacing of the first and second optical beams is
determined by an angle of the first prism wedge pair and the second
prism wedge pair and a first focal length of the first focusing
lens and a second focal length of the second focusing lens.
In some embodiments, the first collimating lens is spaced a first
distance from the first optical source, the first distance
corresponding to a focal length of the first collimating lens. In
some embodiments, the output lens creates an angular separation
between the first optical beam and the second optical beam. In some
embodiments, the angular separation between the first optical beam
and the second optical beam is less than two degrees. In some
embodiments, the angular separation between the first and second
optical beams is determined by the second spacing of the first and
second optical beams and a focal length of the output lens.
In some embodiments, a method includes generating a first optical
beam at a first optical source and a second optical beam at a
second optical source, the first optical beam and the second
optical beam being separated by a first spacing, reducing, by an
optical system, the first spacing between the first optical beam
and the second optical beam to a second spacing, and transmitting
the first optical beam and the second optical beam to an output
lens at the second spacing. In some embodiments, the optical system
includes a first prism wedge pair to modify a first decenter of the
first optical beam with respect to the output lens and a second
prism wedge pair to modify a second decenter of the second optical
beam with respect to the output lens.
In some embodiments, reducing the first spacing between the first
optical beam and the second optical beam includes collimating the
first optical beam using a first collimating lens, redirecting the
first optical beam using a first prism wedge, focusing the first
optical beam on a second prism wedge using a first focusing lens,
and redirecting the first optical beam toward the output lens using
the second prism wedge.
In some embodiments, reducing the first spacing between the first
and second optical beams further includes collimating the second
optical beam using a second collimating lens, redirecting the
second optical beam using a third prism wedge, focusing the second
optical beam on a fourth prism wedge using a second focusing lens,
and redirecting the second optical beam toward the output lens
using the fourth prism wedge. In some embodiments, the second
spacing of the first and second optical beams is determined by an
angle of the first prism wedge pair and the second prism wedge pair
and a first focal length of the first focusing lens and second
focal length of the second focusing lens. In some embodiments, the
first collimating lens is spaced a first distance from the first
optical source, the first distance corresponding to a focal length
of the first collimating lens. In some embodiments, the second
prism wedge is spaced a second distance from the first focusing
lens, the second distance corresponding to a focal length of the
first focusing lens.
In some embodiments, the method further includes creating an
angular separation of the first optical beam and second optical
beam using the output lens. In some embodiments, the angular
separation is based on the second spacing of the first optical beam
and the second optical beam. In some embodiments, the angular
separation between the first optical beam and the second optical
beam is less than two degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the various examples,
reference is now made to the following detailed description taken
in connection with the accompanying drawings in which like
identifiers correspond to like elements.
FIG. 1 illustrates an example FMCW LIDAR system according to
embodiments of the present disclosure.
FIG. 2 is a time-frequency diagram illustrating an example of FMCW
LIDAR waveforms according to embodiments of the present
disclosure.
FIG. 3 is a block diagram of an example LIDAR system according to
embodiments of the present disclosure.
FIG. 4 is a block diagram of an example optical system according to
embodiments of the present disclosure.
FIG. 5A is an illustration of optical beam spacing at an optical
source array according to embodiments of the present
disclosure.
FIG. 5B is an illustration of optical beam spacing at an image
conjugate position according to embodiments of the present
disclosure.
FIG. 5C is an illustration of an output optical beam separation
according to embodiments of the present disclosure.
FIG. 6 is a flow diagram of an example method for reducing image
conjugate pitch according to embodiments of the present
disclosure.
FIG. 7 is a block diagram of another example optical system to
reduce image conjugate pitch according to embodiments of the
present disclosure.
DETAILED DESCRIPTION
The present disclosure describes various examples of LIDAR systems
and methods for image conjugate pitch reduction. According to some
embodiments, the described LIDAR system may be implemented in any
sensing market, such as, but not limited to, transportation,
manufacturing, metrology, medical, and security systems. According
to some embodiments, the described LIDAR system is implemented as
part of a front-end of frequency modulated continuous-wave (FMCW)
device that assists with spatial awareness for automated driver
assist systems, or self-driving vehicles.
The present disclosure addresses the above issues associated with
adding additional optical beams to a single output lens of a LIDAR
system by reducing the pitch (i.e., spacing) between the optical
beams prior to reaching the output lens. In one example, the
present disclosure reduces the pitch using a dual prism
architecture with a collimating lens and a focusing lens for each
of the optical beams. The collimating lens may first collimate an
optical beam into a first prism wedge. The prism may angle the
optical beam towards the focusing lens (i.e., toward a center axis
of the output lens) which may focus the optical beam on a front
surface of a second prism wedge. The second prism wedge may
redirect the optical beam toward the output lens at a reduced
decenter resulting in reduced spacing between optical beams. The
reduced spacing between optical beams may reduce aberrations in the
output beams and may also provide for reduced angular separation
between the output optical beams.
FIG. 1 illustrates a LIDAR system 100 according to example
implementations of the present disclosure. The LIDAR system 100
includes one or more of each of a number of components, but may
include fewer or additional components than shown in FIG. 1. As
shown, the LIDAR system 100 includes optical circuits 101
implemented on a photonics chip. The optical circuits 101 may
include a combination of active optical components and passive
optical components. Active optical components may generate,
amplify, and/or detect optical signals and the like. In some
examples, the active optical component includes optical beams at
different wavelengths, and includes one or more optical amplifiers,
one or more optical detectors, or the like.
Free space optics 115 may include one or more optical waveguides to
carry optical signals, and route and manipulate optical signals to
appropriate input/output ports of the active optical circuit. The
free space optics 115 may also include one or more optical
components such as taps, wavelength division multiplexers (WDM),
splitters/combiners, polarization beam splitters (PBS),
collimators, couplers or the like. In some examples, the free space
optics 115 may include components to transform the polarization
state and direct received polarized light to optical detectors
using a PBS, for example. The free space optics 115 may further
include a diffractive element to deflect optical beams having
different frequencies at different angles along an axis (e.g., a
fast-axis).
In some examples, the LIDAR system 100 includes an optical scanner
102 that includes one or more scanning mirrors that are rotatable
along an axis (e.g., a slow-axis) that is orthogonal or
substantially orthogonal to the fast-axis of the diffractive
element to steer optical signals to scan an environment according
to a scanning pattern. For instance, the scanning mirrors may be
rotatable by one or more galvanometers. Objects in the target
environment may scatter an incident light into a return optical
beam or a target return signal. The optical scanner 102 also
collects the return optical beam or the target return signal, which
may be returned to the passive optical circuit component of the
optical circuits 101. For example, the return optical beam may be
directed to an optical detector by a polarization beam splitter. In
addition to the mirrors and galvanometers, the optical scanner 102
may include components such as a quarter-wave plate, lens,
anti-reflective coated window or the like.
To control and support the optical circuits 101 and optical scanner
102, the LIDAR system 100 includes LIDAR control systems 110. The
LIDAR control systems 110 may include a processing device for the
LIDAR system 100. In some examples, the processing device may be
one or more general-purpose processing devices such as a
microprocessor, central processing unit, or the like. More
particularly, the processing device may be complex instruction set
computing (CISC) microprocessor, reduced instruction set computer
(RISC) microprocessor, very long instruction word (VLIW)
microprocessor, or processor implementing other instruction sets,
or processors implementing a combination of instruction sets. The
processing device may also be one or more special-purpose
processing devices such as an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA), a digital
signal processor (DSP), network processor, or the like.
In some examples, the LIDAR control systems 110 may include a
signal processing unit 112 such as a DSP. The LIDAR control systems
110 are configured to output digital control signals to control
optical drivers 103. In some examples, the digital control signals
may be converted to analog signals through signal conversion unit
106. For example, the signal conversion unit 106 may include a
digital-to-analog converter. The optical drivers 103 may then
provide drive signals to active optical components of optical
circuits 101 to drive optical sources such as lasers and
amplifiers. In some examples, several optical drivers 103 and
signal conversion units 106 may be provided to drive multiple
optical sources.
The LIDAR control systems 110 are also configured to output digital
control signals for the optical scanner 102. A motion control
system 105 may control the galvanometers of the optical scanner 102
based on control signals received from the LIDAR control systems
110. For example, a digital-to-analog converter may convert
coordinate routing information from the LIDAR control systems 110
to signals interpretable by the galvanometers in the optical
scanner 102. In some examples, a motion control system 105 may also
return information to the LIDAR control systems 110 about the
position or operation of components of the optical scanner 102. For
example, an analog-to-digital converter may in turn convert
information about the galvanometers' position to a signal
interpretable by the LIDAR control systems 110.
The LIDAR control systems 110 are further configured to analyze
incoming digital signals. In this regard, the LIDAR system 100
includes optical receivers 104 to measure one or more beams
received by optical circuits 101. For example, a reference beam
receiver may measure the amplitude of a reference beam from the
active optical component, and an analog-to-digital converter
converts signals from the reference receiver to signals
interpretable by the LIDAR control systems 110. Target receivers
measure the optical signal that carries information about the range
and velocity of a target in the form of a beat frequency, modulated
optical signal. The reflected beam may be mixed with a second
signal from a local oscillator. The optical receivers 104 may
include a high-speed analog-to-digital converter to convert signals
from the target receiver to signals interpretable by the LIDAR
control systems 110. In some examples, the signals from the optical
receivers 104 may be subject to signal conditioning by signal
conditioning unit 107 prior to receipt by the LIDAR control systems
110. For example, the signals from the optical receivers 104 may be
provided to an operational amplifier for amplification of the
received signals and the amplified signals may be provided to the
LIDAR control systems 110.
In some applications, the LIDAR system 100 may additionally include
one or more imaging devices 108 configured to capture images of the
environment, a global positioning system 109 configured to provide
a geographic location of the system, or other sensor inputs. The
LIDAR system 100 may also include an image processing system 114.
The image processing system 114 can be configured to receive the
images and geographic location, and send the images and location or
information related thereto to the LIDAR control systems 110 or
other systems connected to the LIDAR system 100.
In operation according to some examples, the LIDAR system 100 is
configured to use nondegenerate optical sources to simultaneously
measure range and velocity across two dimensions. This capability
allows for real-time, long range measurements of range, velocity,
azimuth, and elevation of the surrounding environment.
In some examples, the scanning process begins with the optical
drivers 103 and LIDAR control systems 110. The LIDAR control
systems 110 instruct the optical drivers 103 to independently
modulate one or more optical beams, and these modulated signals
propagate through the passive optical circuit to the collimator.
The collimator directs the light at the optical scanning system
that scans the environment over a preprogrammed pattern defined by
the motion control system 105. The optical circuits 101 may also
include a polarization wave plate (PWP) to transform the
polarization of the light as it leaves the optical circuits 101. In
some examples, the polarization wave plate may be a quarter-wave
plate or a half-wave plate. A portion of the polarized light may
also be reflected back to the optical circuits 101. For example,
lensing or collimating systems used in LIDAR system 100 may have
natural reflective properties or a reflective coating to reflect a
portion of the light back to the optical circuits 101.
Optical signals reflected back from the environment pass through
the optical circuits 101 to the receivers. Because the polarization
of the light has been transformed, it may be reflected by a
polarization beam splitter along with the portion of polarized
light that was reflected back to the optical circuits 101.
Accordingly, rather than returning to the same fiber or waveguide
as an optical source, the reflected light is reflected to separate
optical receivers. These signals interfere with one another and
generate a combined signal. Each beam signal that returns from the
target produces a time-shifted waveform. The temporal phase
difference between the two waveforms generates a beat frequency
measured on the optical receivers (photodetectors). The combined
signal can then be reflected to the optical receivers 104.
The analog signals from the optical receivers 104 are converted to
digital signals using ADCs. The digital signals are then sent to
the LIDAR control systems 110. A signal processing unit 112 may
then receive the digital signals for further processing. In some
embodiments, the signal processing unit 112 also receives position
data from the motion control system 105 and galvanometers (not
shown) as well as image data from the image processing system 114.
The signal processing unit 112 can then generate 3D point cloud
data with information about range and velocity of points in the
environment as the optical scanner 102 scans additional points. The
signal processing unit 112 can also overlay 3D point cloud data
with the image data to determine velocity and distance of objects
in the surrounding area. The system also processes the
satellite-based navigation location data to provide a precise
global location.
FIG. 2 is a time-frequency diagram 200 of an FMCW scanning signal
201 that can be used by a LIDAR system, such as system 100, to scan
a target environment according to some embodiments. In one example,
the scanning waveform 201, labeled as f.sub.FM(t), is a sawtooth
waveform (sawtooth "chirp") with a chirp bandwidth .DELTA.f.sub.C
and a chirp period T.sub.C. The slope of the sawtooth is given as
k=(.DELTA.f.sub.C/T.sub.C). FIG. 2 also depicts target return
signal 202 according to some embodiments. Target return signal 202,
labeled as f.sub.FM(t-.DELTA.t), is a time-delayed version of the
scanning signal 201, where .DELTA.t is the round trip time to and
from a target illuminated by scanning signal 201. The round trip
time is given as .DELTA.t=2R/v, where R is the target range and v
is the velocity of the optical beam, which is the speed of light c.
The target range, R, can therefore be calculated as
R=c(.DELTA.t/2). When the return signal 202 is optically mixed with
the scanning signal, a range dependent difference frequency ("beat
frequency") .DELTA.f.sub.R(t) is generated. The beat frequency
.DELTA.f.sub.R(t) is linearly related to the time delay .DELTA.t by
the slope of the sawtooth k. That is, .DELTA.f.sub.R(t)=k.DELTA.t.
Since the target range R is proportional to .DELTA.t, the target
range R can be calculated as R=(c/2)(.DELTA.f.sub.R(t)/k). That is,
the range R is linearly related to the beat frequency
.DELTA.f.sub.R(t). The beat frequency .DELTA.f.sub.R(t) can be
generated, for example, as an analog signal in optical receivers
104 of system 100. The beat frequency can then be digitized by an
analog-to-digital converter (ADC), for example, in a signal
conditioning unit such as signal conditioning unit 107 in LIDAR
system 100. The digitized beat frequency signal can then be
digitally processed, for example, in a signal processing unit, such
as signal processing unit 112 in system 100. It should be noted
that the target return signal 202 will, in general, also includes a
frequency offset (Doppler shift) if the target has a velocity
relative to the LIDAR system 100. The Doppler shift can be
determined separately, and used to correct the frequency of the
return signal, so the Doppler shift is not shown in FIG. 2 for
simplicity and ease of explanation. It should also be noted that
the sampling frequency of the ADC will determine the highest beat
frequency that can be processed by the system without aliasing. In
general, the highest frequency that can be processed is one-half of
the sampling frequency (i.e., the "Nyquist limit"). In one example,
and without limitation, if the sampling frequency of the ADC is 1
gigahertz, then the highest beat frequency that can be processed
without aliasing (.DELTA.f.sub.Rmax) is 500 megahertz. This limit
in turn determines the maximum range of the system as
R.sub.max=(c/2)(.DELTA.f.sub.Rmax/k) which can be adjusted by
changing the chirp slope k. In one example, while the data samples
from the ADC may be continuous, the subsequent digital processing
described below may be partitioned into "time segments" that can be
associated with some periodicity in the LIDAR system 100. In one
example, and without limitation, a time segment might correspond to
a predetermined number of chirp periods T, or a number of full
rotations in azimuth by the optical scanner.
FIG. 3 illustrates an example LIDAR system 300 to reduce a pitch
(i.e., spacing) of optical beams provided to a single output
collimating lens. Optical system 300 includes an optical source
array 310, pitch reduction optics 320, and an output lens 330. The
optical source array 310 may include several optical sources that
are separated by a certain spacing, referred to as pitch. Reducing
the pitch between optical sources is desirable in order to provide
for more optical sources at the output lens 330, to reduce
aberrations due to large decenter at the output lens 330 and to
reduce an output angle 340 between the optical beams. In one
embodiment, the pitch between the optical beams may be reduced
using pitch reduction optics 320. Pitch reduction optics 320 may
receive optical beams at a first pitch corresponding to the pitch
of the optical sources and reduce the pitch between the optical
beams prior to reaching the output lens 330. The reduced pitch may
provide for smaller decenter of each of the optical beams at the
output lens 330, resulting in a smaller output angle 340 between
the optical beams without changing the focal length of the output
lens 330. The pitch reduction optics 320 may include free space
optics (e.g., free space optics 115 described in FIG. 1), silicon
optics, or any other type of optics to redirect the optical beams
in a manner that reduces the pitch between the optical beams. An
example embodiment of pitch reduction optics 320 is described in
more detail below with respect to FIG. 4. The LIDAR system 300 may
also include scanner optics 350, such as one or more galvo mirrors
to scan a field of view (FOV) of the LIDAR system 300.
The pitch of the optical beams received at the output lens 330 may
determine the output angle 340 at which the optical beams will be
transmitted from the LIDAR system 300. The output angle may also
depend on the focal length of the output lens. For example, the
output angle separation between beams may be calculated from
equation (1) below:
.theta..times..times. ##EQU00001## where .theta. is the output
angle 340 between optical beams, pitch is the spacing between the
optical beams, n is the number of optical beams, and FL is the
focal length of the output lens 330. The reduced pitch between the
optical beams may provide for an output angle of less than two
degrees. In some embodiments, the reduced pitch may provide for an
output angle of less than one degree.
FIG. 4 illustrates an example optical system 400 to reduce a pitch
of optical beams provided to a single output collimating lens.
Optical system 400 includes an optical source array 401 to produce
several optical beams. Although FIG. 4 depicts only two optical
sources generating two corresponding optical beams, the optical
source array 401 may include any number of optical sources in
either a one-dimensional or two-dimensional array. In one
embodiment, optical source array 401 may include three or more
optical sources. LIDAR system 400 further includes optics to
redirect one or more optical beams and to reduce the decenter of
each optical beam on an output lens 410. The optics to redirect
each optical beam may include a collimating lens 402A-B, a first
prism wedge 404A-B, a focusing lens 406A-B, and a second prism
wedge 408A-B.
In one embodiment, collimating lens 402A-B may receive an optical
beam from the optical source array 401 and collimate the optical
beam. The optical beam as collimated may be directed toward the
first prism wedge 404A-B. The second prism wedge 408A-B may
redirect the optical beam in the direction of the output lens
center axis 412 (i.e., in a direction to reduce the decenter of the
optical beam). The reduction in the decenter of each optical beam
may be dependent on the angle of the first prism wedge 404A-B and
the focal length of the focusing lens 406A-B. In one embodiment,
the angle of the first prism wedges 404A-B can be adjusted to
calibrate the decenter of the optical beam and the pitch between
the optical beams. A focusing lens 406A-B may receive the
redirected optical beam from the first prism wedge 404A-B and focus
the optical beam at a front surface of a second prism wedge 408A-B.
The second prism wedges 408A-B may redirect the optical beam toward
the output lens 410. The second prism wedges 408A-B may redirect
the optical beam to be parallel with the output lens center axis
412 and each of the other optical beams. Therefore, as can be seen
from FIG. 4, each optical beam from the optical source array 401
may be redirected to have a reduced decenter on the output lens 410
than would be provided by the pitch of the optical sources of the
optical source array 401.
In one embodiment, a local oscillator (LO) may be generated at the
front surface of the second prism wedge 408A-B. For example, the
front surface of the second prism wedge 408A-B may be partially
reflective (e.g., a partially reflective coating, surface, etc.).
Therefore, a portion of the optical beam may be reflected by the
second prism wedge 408A-B as an LO of the optical beam.
FIG. 5A depicts a cross-sectional view of an exemplary optical beam
pitch at the optical source array 401 in accordance with FIG. 4.
The optical beam pitch (i.e., spacing) at the optical source array
401 may be limited by the structure of the optical sources and
manufacturing constraints of the optical beam array.
FIG. 5B depicts a cross-sectional view of an exemplary optical beam
pitch at the source conjugate position after pitch reduction. The
source conjugate position as depicted may be directly after the
second wedge 408A-B, as depicted in FIG. 4. The dashed circles
depicted in FIG. 5A may illustrate the pitch at which the optical
beams would be at without the optical system (e.g., optical system
400) to reduce the optical beam pitch. Therefore, as shown, the
optical beam pitch at the source conjugate position may be reduced
as compared to the optical beam pitch at the optical source array
(e.g., optical source array 401).
FIG. 5C illustrates an example of the optical beam at an output of
LIDAR systems described herein according to some embodiments. The
optical beam separation at the LIDAR output may be directly
dependent on the pitch between the optical beams at the source
conjugate position, and accordingly the decenter of each beam
incident on the output lens (e.g., output lens 410 of FIG. 4).
FIG. 6 is a flowchart illustrating an example method 600 in a LIDAR
system for image conjugate pitch reduction.
With reference to FIG. 6, method 600 illustrates example functions
used by various embodiments. Although specific function blocks
("blocks") are disclosed in method 600, such blocks are examples.
That is, embodiments are well suited to performing various other
blocks or variations of the blocks recited in method 600. It is
appreciated that the blocks in method 600 may be performed in an
order different than presented, and that not all of the blocks in
method 600 may be performed.
Method 600 begins at block 610, where a first optical source
generates a first optical beam and a second optical source
generates a second optical beam. The first and second optical beams
may be separated by a first spacing. The first spacing may
correspond to the spacing of the first and second optical sources.
A chief ray of each of the first and second optical beams may be
substantially parallel to one another.
At block 620, an optical system reduces the first spacing between
the first and second optical beams to a second spacing. The optical
system may include several sets of optics to redirect each optical
beam. For example, the optical system may include a first set of
optics to reduce a decenter of a first optical beam and a second
set of optics to reduce a decenter of the second optical beam. Each
set of optics may include at least a prism wedge pair to change the
direction of the optical beams. The sets of optics may also include
a collimating lens to first collimate the optical beams toward a
first prism wedge of a prism wedge pair. The first prism wedge may
direct the optical beam to a focusing lens. The focusing lens may
focus the optical beam at a front surface of a second prism wedge.
The second prism wedge may be complimentary to the first prism
wedge to redirect the optical beam toward the output lens on a
trajectory parallel to the original optical beam generated by the
optical source.
At block 630, the optical system transmits the first and second
optical beams to an output lens. The output lens may provide an
angular separation between the first and second optical beams. The
angular separation may depend on the spacing between the first and
second optical beams. The angular separation may provide for
distinct lines to scan a scene in the FOV of the LDAR system to
avoid overlap of collected data points.
FIG. 7 illustrates another example embodiment of an optical system
700 to reduce a pitch of optical beams provided to a single output
collimating lens 702. Optical system 700 includes an optical source
array 701 including four optical sources and associated sets of
optics to reduce the pitch of the optical beams generated by the
optical sources. In one embodiment, each set of optics includes a
wedge pair to reduce the decenter of each optical beam and the
separation between the four optical beams. The inner wedge pairs
710 and 715 may have wedge angles to reduce the pitch of the inner
optical beams by a particular distance. The outer wedge pairs 705
and 720 may have larger wedge angles to reduce the pitch of the
outer optical beams by a larger distance than the inner wedges. The
larger wedge angles of the outer wedge pairs 705 and 720 may
provide for similar spacing between each of the optical beams at
the output lens. It should be noted that optical system 700 may be
extended to any number of optical sources as well as any
combination of optics to reduce the pitch of the optical sources in
focal space. As additional optical sources are added in parallel,
the wedge angles of the optics for the additional sources may be
increased accordingly as they are further from center.
The preceding description sets forth numerous specific details such
as examples of specific systems, components, methods, and so forth,
in order to provide a thorough understanding of several examples in
the present disclosure. It will be apparent to one skilled in the
art, however, that at least some examples of the present disclosure
may be practiced without these specific details. In other
instances, well-known components or methods are not described in
detail or are presented in simple block diagram form in order to
avoid unnecessarily obscuring the present disclosure. Thus, the
specific details set forth are merely exemplary. Particular
examples may vary from these exemplary details and still be
contemplated to be within the scope of the present disclosure.
Any reference throughout this specification to "one example" or "an
example" means that a particular feature, structure, or
characteristic described in connection with the examples are
included in at least one example. Therefore, the appearances of the
phrase "in one example" or "in an example" in various places
throughout this specification are not necessarily all referring to
the same example.
Although the operations of the methods herein are shown and
described in a particular order, the order of the operations of
each method may be altered so that certain operations may be
performed in an inverse order or so that certain operation may be
performed, at least in part, concurrently with other operations.
Instructions or sub-operations of distinct operations may be
performed in an intermittent or alternating manner.
The above description of illustrated implementations of the
invention, including what is described in the Abstract, is not
intended to be exhaustive or to limit the invention to the precise
forms disclosed. While specific implementations of, and examples
for, the invention are described herein for illustrative purposes,
various equivalent modifications are possible within the scope of
the invention, as those skilled in the relevant art will recognize.
The words "example" or "exemplary" are used herein to mean serving
as an example, instance, or illustration. Any aspect or design
described herein as "example" or "exemplary" is not necessarily to
be construed as preferred or advantageous over other aspects or
designs. Rather, use of the words "example" or "exemplary" is
intended to present concepts in a concrete fashion. As used in this
application, the term "or" is intended to mean an inclusive "or"
rather than an exclusive "or". That is, unless specified otherwise,
or clear from context, "X includes A or B" is intended to mean any
of the natural inclusive permutations. That is, if X includes A; X
includes B; or X includes both A and B, then "X includes A or B" is
satisfied under any of the foregoing instances. In addition, the
articles "a" and "an" as used in this application and the appended
claims should generally be construed to mean "one or more" unless
specified otherwise or clear from context to be directed to a
singular form. Furthermore, the terms "first," "second," "third,"
"fourth," etc. as used herein are meant as labels to distinguish
among different elements and may not necessarily have an ordinal
meaning according to their numerical designation.
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